Hitherto, an image pickup apparatus that picks up images of an object by radiating infrared radiation to the object and capturing light reflected by the object has been known from, for example, Japanese Unexamined Patent Application Publication No. 2-304680.
Such an image pickup apparatus can determine a difference between an image obtained when infrared radiation is not radiated and an image obtained when infrared radiation is radiated. When infrared radiation is not radiated, external light impinges on the object and is reflected by the object. Thus, light picked up by the image pickup apparatus is only an external light component. In contrast when infrared radiation is radiated, external light and infrared radiation impinge on the object and are reflected by the object. Thus, the light picked up by the image pickup apparatus includes an external light component and an infrared component. The difference between the image obtained when infrared radiation is not radiated and the image obtained when infrared radiation is radiated is an image in which the external light component is canceled and only the infrared component is extracted. Accordingly, this image pickup apparatus can obtain an image in which the influence of external light is suppressed.